Method for stabilizing nitrocellulose



Dec. 28, 1937. M. G. MILLIKEN METHOD FOR S'TABILIZING NITROCELLULOSE Filed 0G13. 27, 1954 touted Dec. 28, 1937 Mahlon G. Milliken, Wilmington, Del., assigner to Hercules Powder Company, Wilmington, in a corporation oi Delaware Application Uctober 27, 1934, Serial No. 750,258

8 Claims.

This invention relates to a method and apparatus for stabilizing nitrocellulose.

Heretofore, as is well known, in the production of nitrocellulose, as nitrated cotton, it has been the practice to eect nitration of puried cellulose, wash the nitrated product almost free of acid and then boil the product to stabilize it by the removal of residual dilute acid.

The boiling or stabilizing treatment has heretoiore been carried out in large tubs under atmospheric pressures, the necessary heat being supplied by steam introduced into the bottom of the tubs. Such procedure is disadvantageous, especially in that it is time consuming, requiring as much as fty hours for nitrocellulose of high nitration, and hence for any substantial production a large amount of equipment is required with consequent high capital and maintenance cost.

Now in accordance with this invention, there is provided a method and apparatus wherebyl the stabilizing treatment of nitrocellulose is effected wlthi great eiliciency and with a large saving in time and consequent saving in cost.

Generally speaking, in accordance with this invention the stabilization of nitrocellulose is effected in a continuous or semi-continuous manner, at a pressure above atmospheric and at a temperature substantially above the normal boiling point of the dilute acid to be removed from the nitrocellulose. In proceeding in accordance with this invention, the primary effect upon the nitrocellulose is its stabilization and while some slight reduction in viscosity may occur, such is incidental.

The apparatus in accordance with this invention comprises, generally speaking, a passage through which the nitrocellulose is passed, the passage providing charging and discharging zones and a treating zone in which the nitrocellulose, together with water, is subjected to a hydrostatic pressure and to an elevated temperature. Means are provided for feeding nitrocellulose to the passage continuously or periodically and in a manner such that the nitrocellulose will progress through the passage with continuous or intermittent movement.

Having now indicated in a general way the nature and purpose of this invention, I shall proceed to a detailed description thereof with reference to the accompanying drawing, in which is illustrated a preferred form of apparatus embodying this invention, in connection with a description of which the method embodying this invention will be described, and in which:

Figure 1 is a diagrammatic view of a form of apparatus embodying this invention and adaptable for carrying out the invention thereof.

Figure 2 is a view, partly in section, showing the arrangement of the inlet to the apparatus shown in Figure l. f

In the drawing the apparatus shown comprises a U-shaped passage or tube, circular in cross section, one leg A of which, extending vertically, forms an inlet zone. The leg A may be closed at its top, or alternatively it may be left open. The second leg B, extending vertically, forms a discharge zone, while the base C, extending horizontally, forms a treating zone.

The charging leg or zone A is of greater height than the discharging leg or zone B, the difference in height being such as to overcome friction in the passage, so that nitrocellulose introduced into the charging zone may force previously introduced nitrocellulose through the treating zone and out of the discharging zone.

'Ihe charging leg or zone A is provided, at its upper end, with an inlet opening d, so positioned that nitrocellulose entering through a charging line e, in the form of a slurry in admixture with water, will enter on a tangent to the circumference and at right angles to the axis of the charging leg or zone, as shown in Figure 2. charging line is connected through any suitable pump, not shown, with a supply of nitrocellulose slurry in any suitable container, not shown.

'I'he treating leg or zone C is provided with steam injection nozzles f, f, positioned adjacent its inlet end and at/intervals along the leg C so vas to maintain desired temperature in the treating zone. The nozzles f, f receive steam from any suitable source through a conduit g. A cold water jet 1:, receiving water from any suitable source, will desirably be provided in the leg B below the cooler, or near the discharge end of zone CL The discharge leg or zone B is provided adjacent its upper end with a cooling jacket h, through which water is circulated, thewater being introduced into the upper end of the jacket, through a pipe i, and being discharged from the lower end, through a pipe i'. Alternatively, the cooling may be eiected by the provision of a cooling jacket about the discharge end portion of the treating zone C. The cooling water may, if desired, extend into the lower end of jacket h and discharged from the upper end.

The

CII

The discharge leg or zone B ls arranged to discharge into a flume y', by which the nitrocellulose slurry is carried to any suitable receiver, not shown.

Clean-out plugs y, y are provided at appropriate points in the legs A, B and C in order to allow clean-out in the event of a jam.

In practice, using the apparatus described above, nitrocellulose slurry is introduced into the leg or zone A through inlet d, the apparatus having been previously filled with water or dilute acid. The slurry enters the leg A with a rotary motion, which causes the' nitrocellulose to mat itself uniformly and form a loosely compacted plug, which conforms to the cross section of the leg and which moves downward through the leg or zone A and into the treating zone C, wherein it is under the hydrostatic pressure, above atmospheric, of the columns in the legs or zones A and B and wherein it is subjected to an elevated temperature through the introduction of steam through the nozzles f, f.

With continued supply of slurry to the leg or zone A, it will be observed that the nitrocellulose, loosely matted, will be forced through the treating zone and up and out of the discharging leg or zone B.

In practice, however, nitrocellulose slurry is fed into the leg or zone A in increments intermittently and consequently passed through the treating zone with intermittent movement and discharged from the leg or zone B, intermittently, in increments corresponding to the increments `fed into leg A, in order to allow the nitrocellulose in the treating zone to remain therein a suiiicient time to accomplish its stabilization.

As more specifically illustrative, for example, the U-shaped passage, formed from a low carbon steel lined with a veneer of stainless steel (Plykrome) andof suitable thickness to withstand pressure, may have a diameter of twenty inches. The leg or zone A may have a` height, from the axis of the zone C to the inlet opening d, of 45 feet, while the leg or zone B may have a height of 35 feet. The 10 foot head of leg A will overcome friction. The treating zone C may have a length of 600 feet and steam may be introduced through nozzles f, f at say 250 F. to maintain a temperature of say about 240 F. in the treating zone. The hydrostatic pressure in the treating zone will be about 15 pounds. The temperature will be above the normal boiling point of water but below that at which water will boil under the pressure obtaining in the treating zone.

Now assuming that a nitrated cotton of about 13.40% nitrogen, such as would require about hours to stabilize by former methods, is to be treated and that the U-shaped passage has been filled with water, about 450 pounds of the nitrocotton in water (say 13 parts of water to 1 part nitrocotton) is pumped into the charging leg A over a period of about live minutes. The nitrocotton mats and forms a plug, which drops into the treating zone, to which steam is admitted.

At intervals of an hour further increments of 450 pounds each are pumped into the leg A, over periods of five minutes. As the increments are entered into the apparatus, previously entered increments are advanced through the reaction zone untilafter twelve hours an increment of 450 pounds of completely stabilized nitrocotton, cooled by the cooling jacket h to a temperature such that the Water will not boil on release of the pressure, i. e. below the normal boiling point of water, is discharged from leg B into fiume i,

as an increment is pumped intc` leg A.v Thereafter an increment will be entered into and one discharged from the apparatus every hour.

It will be noted that each increment of nitrocellulose remains in the apparatus for twelve hours and since the legs or zones A and B each hold about 450 pounds of nitrocellulose, the lncrements will be in the reaction zone for ten hours. i

From the example given, it will be observed that complete stabilization of nitrated cellulose of 13.40% nitrogen content is effected in ten hours as compared with 50 hours required heretofore. Comparable saving in time is effected in the stabilization of nitrocellulose of various nitrogen content.

The above detailed description of the carrying out of this invention involves semi-continuous precedure; however, it will be understood that the method may be readily carried out in a 4continuous manner by providing for a continuous `supply of nitrocellulose and water to the leg A through-the conduit e. Continuous supply of nitrocellulosev and water will result in continuous discharge thereof. For continuous operation the apparatus described will obviously be enlarged by lengtheningfthe treating zone C to a length with reference to the rate of feed so that the nitrocellulose will be in that zone for the requisite time, and by increasing the difference in heighth between the charging leg A and the discharging leg B.

It will be understood that while in the detailed description above the use of water in admlxture with the nitrocellulose has been indicated, the water acts as a carrier for the nitrocellulose and that any other liquid which will actas a carrier and which is inert to the nitrocellulose under the treatment given in the zone C will be equivalent for water and is contemplated as an equivalent therefor within the scope of the claims appended hereto. v

It will be understood that it is not intended that this invention shall be in any wise limited in scope by the detailed description of method and l apparatus contained herein, since various and sundry modifications in details may be made within the scope of the invention.

While this invention has been described more particularly with reference to the stabilization of nitrocellulose, it will be appreciated that the method and apparatus in accordance with the invention, are adapted for the treatment of any cellulose ester or ether in a fibrous condition or one which has been used in a condition approximating a fibrous condition, or other form lending them to matting in the formation of plugs through entry into the apparatus with a rotary motion as described, and that it is contemplated that in the treatment of cellulose esters and ethers they may be used for the treatment of such esters and ethers and that where adaptable the vtreatment of such esters and ethers is contemplated as embraced within thescope of this in.

vention.

The method and apparatus in accordance with this invention is possessed of very great practical advantage in that it not only very largely lreduces the time necessary for the stabilization of nitrocellulose and where adaptable to the treatment of other cellulose esters and ethers will be found efcient, but provides for the stabilization, more particularly, of nitrocellulose with very largely increased safety in operation over stabilization in an autoclave, as practiced by the prior art.

From the standpoint of safety, it will be noted that the surface of the liquid in the apparatus is under atmospheric pressure only so that, as will be obvious, should there be any sudden evolution of gases from any decomposition of nitrocellulose under treatment in the apparatus, suchgases will be able to escape harmlessly upon the development of .only suiiicient pressure to force out of the apparatus the column of liquid in one or both of the vertical legs A and B of the apparatus. Thus, it will be obvious that on the evolution of gas from any decomposition of l nitrocellulose in the apparatus, pressure will be automatically relieved before it can rise to a point such as to disrupt the apparatus in explosive force.

In distinctiomwhere decomposition of nitrocellulose occurs inthe autoclaves of the prior art,

pressure from evolved gases is only released by a bursting of the autoclave.

No claim is made herein for the apparatus described herein, since such forms the subject matter of an application for patent filed by me as a division hereof, Serial No. 8,479, filed Feb. 27, 1935.

What I claim and desire to protect by Letters Patent is:

1. A method of stabilizing nitrocellulose fibers which comprises subjecting nitrocellulose fibers admixed with water to an increasing and then decreasing hydrostatic pressure, which is above atmospheric pressure, and to a controlled heating, by means of open steam, for a time suiiicient to stabilize the nitrocellulose and remove residual dilute acid therefrom and to a temperature above the boiling point of water when at atmospheric pressure but below the temperature at which water will boil under the superimposed hydrostatic pressure.

2. A method of stabilizing nitrocellulose fibers which comprises subjecting nitrocellulose fibers admixed with water to an increasing and then decreasing hydrostaticpressure, which is above atmospheric pressure, and to a controlled heating, by means oi open steam, for a time sufiicient to stabilize the nitrocellulose and remove residual dilute acid therefrom and to a temperature above the boiling point of water when at atmospheric pressure but below the temperature at which water will boil under the superimposed hydrostatic pressure, and then cooling the mixture of nitrocellulose fibers and water to a temperature which isbelow the boiling point of water when at atmospheric pressure, and releasing the superimposed hydrostatic pressure.

3. A method for stabilizing nitrocellulose fibers which comprises introducing a mixture of said fibers and water intermittently into a conned passageway, permitting the nitrocellulose bers to settle and form plugs of fibers under an intime sufficient to stabilize the nitrocellulose and remove residual dilute acid therefrom and then subjecting the nitrocellulose fibers to decreasing hydrostatic pressure and discharging the stabilized nitrocellulose at atmospheric pressure.

4. The method of claim 3 in which the step of heating to an elevated but controlled temperature is 'performed by the use of open steam.

5. A method of stabilizing nitrocellulose fibers which comprises continuously introducing a mixture of nitrocellulose fibers and water into a confined passageway, permitting the nitrocellulose fibers tosettle within the confined passage- -Way and to form plugs of fibers, the nitrocellulose while settling being subjected to an increasing hydrostatic pressure, heating the nitrocellulose to an elevated but controlled temperature for a time suflicient to stabilize the nitro-k cellulose and remove residual dilute acid therefrom, then decreasing the hydrostatic pressure superimposed upon the nitrocellulose anddischarging the nitrocellulose at atmospheric pressure.

6. The method of claim 5 in which the step of heating the nitrocellulose plugs is performed by the use of open steam.

'1. A method of stabilizing nitrocellulose which comprises introducing a mixture of nitrocellulose fibers and water into a vertical confined passageway, permitting the nitrocellulose fibers to settle within the said passageway and to form plugs of nitrocellulose fibers, progressively moving said plugs to the bottom of the vertical confined passageway thence into a horizontal pasageway maintained under a hydrostatic pressure of about 30 pounds per square inch absolute, heating the said nitrocellulose plugs for a time, sufiicient to stabilize theI nitrocellulose and remove residual acid therefrom by means of open steam introduced into the horizontal passageway, progressively moving said plugs along the horizontal passageway and discharging them into a second vertical passageway, moving the said plugs upwardly in said second passageway under a constantly decreasing-hydrostatic pressure, cooling the nitrocellulose-water mixture within said second passageway and discharging the `nitrocellulose at atmospheric pressure.

8. The method of stabilizing nitrated cellulose which includes introducing nitrated cellulose iibers in admixture with water into a treating zone maintained under hydrostatic pressure, applying steam to the mixture of nitrocellulose fibers and water in the treating zone, heating the mixture for a time sufcient to stabilize the nitrocellulose and remove residual dilute acid therefrom and discharging the stabilized nitrocellulose from the treating zone.

MAI-ILDN G. MILLIKEN. 

